Twinning and Chromosome Anomalies in Kanota Oats 1

The frequency and chromosomec onstitution of twins in three Avena species (2n=42) were determined. A much higher frequency of twin seedlings was obtained from A. byzantina C. Koch var. ‘Kanota’ than from four other varieties of A. sativa L. and A. nuda L. Eighty‐four percent of 44 Kanota twins observed in 1966‐67 consisted of sister seedlings of different size. Seventeen of the 31 surviving smaller sisters and one of the larger ones had anomalous chromosome numbers, namely 63 (triploid) or Jess than 42. Of 86 pairs of Kanota twins in which both memberssu rvived, 36, 35, and 13 pairs were diplodiploid, diplo‐triploid, and diplo‐aneuploidty pes, respectively. One diplo‐haploid twin and one diplo‐diplo.triploid triplet were obtained. Variable numberos f trivalents, bivalents, and univalents were observed at metaphase I in 63‐chromosome plants (triploids). In each cell the number of bivalents and trivalents summedto 21, 22, or 23, which suggests that one or two bivalents were formed by autosyndesis. Twenty‐four percent of the extra 21 chromosomes in triploids failed to pair at metaphase I. These T 1 plants had an average fertility of only 3.5%. Most of their T 2 and T 3 progenies still had more than 42 chromosomes but were markedly higher in fertility. Hypothesesf or the induction of polyembryonic kernels, especially the anomalous twin sister, are presented.